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Energy

Our bodies need energy to grow and repair themselves, keep warm and do physical activity. Energy comes from food and drink, in particular from carbohydrate, protein, fat and alcohol. This energy is measured in kilojoules (kJ) or calories (kcal), with 1 kilocalorie equalling 4.2 kilojoules. In nutrition calorie and kilocalorie are sometimes used to mean the same thing.

Energy values of different nutrients

Carbohydrate

17kJ (4 kcal) per gram

Protein

17kJ (4 kcal) per gram

Fat

37kJ (9 kcal) per gram

Alcohol

29kJ (7 kcal) per gram

As you can see, fat contains more than twice as much energy as carbohydrate and protein, closely followed by alcohol. This needs to be taken into account when we are watching our weight, or trying to reduce it.

Energy density

Food and drinks are made up of different amounts of protein, fat, carbohydrate (and sometimes alcohol); known collectively as macronutrients. The amount of each macronutrient in the food will determine its energy content. Foods that are high in kilojoules per bite, tend to be high in fat and/or sugar (for example, chocolate, fizzy drinks, fats and oils). Such foods are described as energy dense. Low energy dense foods (for example fresh fruit, vegetables and porridge) have fewer kilojoules in each bite and tend to fill you up for longer. But remember it is not only the type of food that we eat but how much – a large plate will have more energy (kilojoules) than a smaller portion.

How much energy do I need?

How much energy you need is dependent on your gender, age, weight, and how active we are. If you are particularly active or play sport, visit our sports nutrition page for information on meeting your energy needs.

Men require more energy than women, and we tend to need less energy as we age due to a decrease in muscle mass. Teenagers have large energy needs to cater for all the growing they are doing.